The present invention relates to a burner provided with an ignition device, which burner is particularly suitable for start-up operations. The invention relates more in particular to such a burner having a built-in ignition device in the form of an auxiliary burner, which is fed with gaseous fuel and air and which is electrically ignited.
For combusting heavy, difficult ignitable fuels, such as pulverized coal, it is common practice to generate a relatively small start-up flame using a fuel which is less likely to blow out and which is used for ignition of the main fuel flow. It is necessary to provide some means for igniting the start-up flame in turn and for maintaining it in a lighted condition during the ignition of the main fuel flow. If the combustion operation is to be carried out in a closed, confined and pressurized space, such as for example in coal gasification processes, the ignition is normally carried out in two steps. First an ignition flame is generated, which flame is used to ignite a gaseous or liquid fuel, thereby producing a second relatively large flame, which in its turn is used to ignite the main fuel flow. The above process for igniting a fuel flow in a pressurized combustion chamber is normally carried out by means of an ignition device and a separate start-up burner operating on gaseous or liquid fuel. The start-up burner is not only used for igniting the main fuel flow but also for pressurizing the combustion chamber before the main fuel is introduced. Prior to introduction of the main fuel flow the iginition device, normally formed by an electrically generated gas torch, and the start-up burner are to be carefully positioned with respect to one another and with respect to the main fuel flow direction. It will be understood that this is a relatively cumbersome operation, in particular since the ignition device and start-up burner are to be installed in openings through the refractory lined wall of a combustion chamber.
A further problem with separate ignition devices and start-up burners, occurs because the ignition devices may be easily damaged due to handling and/or exposure to the radiation in the combustion chamber. Normally, the ignition devices operate with electric sparks, which sparks may be issued from a spark plug in the upstream end of the device. Such a spark plug position is favorable from a point of view of protection against mechanical damage of the plug itself. It is, however, less advisable to have the spark plug arranged at the entry side of the ignition device in view of the thermal load of the device with this position of the spark plug. The whole device is subjected to the high temperature of the flame generated by the sparks emitted from the spark plug.
In order to overcome the above problems caused by the application of ignition devices and separate start-up burners it has been proposed to incorporate such an ignition device in the start-up burner, such that the ignition device is protected against thermal and mechanical shocks by the start-up burner. The known start-up burners with their own ignition devices are, however, quite complicated and cumbersome, the more since such burners should be further provided with appropriate flame detector means. An example of the combination of a burner provided with an ignition device is described in U.S. Pat. No. 4,333,405. In this apparatus the ignition device is substantially centrally arranged in a start-up burner. Although this device as described is a relatively simple construction, it should be noted that the device is not provided with flame detecting means essentially for controlling the operation of the burner. It should be understood that the ignition flame produced in the ignition device can be easily extinguished if the burner should, under these conditions, be interrupted in order to prevent an explosive mixture from collecting in the combustion chamber. The start-up and the operation of the ignition device and of the start-up burner should therefore continuously be monitored.